2 COMPARISON OF WLAN MULTICARRIER DS-SS PHYSICAL LAYER CONFIGURATIONS IN MEASURED INDOOR ENVIRONMENT

The new generation of multimedia laptop and palmtop computing devices is strongly pushing industry towards the development and the implementation of high speed Wireless Local Area Networks (WLANs). This task is not trivial, since the mobility feature has to be provided in a challenging transmission medium such as the indoor radio channel. In this framework the only standards delivered by regulatory bodies are the IEEE 802.11 and the ETSI HIPERLAN [1][2]. Interference and multipath fading are the most significant problems that affect WLANs. WLAN applications often use bands where electronic devices radiate RF energy (e.g. ISM band). In such an environment the interference rejection properties of the Spread Spectrum (SS) technique are precious [3]. Because of this reason the SS technique has been adopted in the IEEE 802.11, both in Direct Sequence (DS) and Frequency Hopping (FH) configurations. Moreover, the adoption of the SS technique allows to gain an intrinsic diversity of the signal in order to cope with the effects of multipath fading. In this paper we show the convenience to combine the SS signaling with the Multicarrier Modulation (MCM), in order to support indoor WLAN applications. The MCM was considered by the ETSI for the HIPERLAN standard, although Decision Feedback Equalization (DFE) was finally adopted. The MCM approach permits to displace the equalization problems fro